Polyaniline/c-mwnt nanocomposite and method for fabricating the same

ABSTRACT

The invention discloses a polyaniline/c-MWNT nanocomposite and a method for fabricating the same. The method comprises the following steps: carboxylating at least one carbon nanotube to form at least one carboxylic carbon nanotube; mixing the at least one carboxylic carbon nanotube with a solvent to form a first carbon nanotube solution; mixing at least one aniline monomer with the first carbon nanotube solution to form a second carbon nanotube solution; mixing an ammonium persulfate solution with the second carbon nanotube solution to form a third carbon nanotube solution; air-extracting and filtering the third carbon nanotube solution to obtain the polyaniline/c-MWNT nanocomposite; cleaning and baking the polyaniline/c-MWNT nanocomposite. The polyaniline/c-MWNT nanocomposite fabricated by the method could be used for electromagnetic shielding or anti-static shielding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a polyaniline/c-MWNTnano-composite and a method for fabricating the same, and moreparticularly, the present invention relates to a polyaniline/c-MWNTnanocomposite which could be used for electromagnetic shielding oranti-static shielding and a method for fabricating the same.

2. Description of the Prior Art

As electronic devices are designed smaller and smaller with higher andhigher density, electronic devices are disturbed more and more seriouslyby electromagnetic waves and radiation frequency. Therefore, theelectron-magnetic compatibility of an electronic device is alwaysconcerned while fabricated, stored, transported and operated. Becauseelectronic devices are broadly applied to various fields including thepeople's livelihood, the national defense and even the space industry,etc, how to avoid the disturbance by electromagnetic waves and radiationfrequency has become the gist of research.

Those electronic devices need avoiding the disturbance ofelectromagnetic waves and radiation frequency could adopt conductingshields to cut off the electromagnetic waves. When electromagnetic wavespass through the shields, the energy of electromagnetic waves would bereflected or absorbed and therefore the disturbance of theelectromagnetic waves could be decreased. In conventional arts,conducting materials are electroplated or coated on plastic casing, orinfilled in plastic casing for electromagnetic shielding. The method ofelectroplating to electroplate metals on casing has disadvantages ofpollution, inconvenience in manufacturing, and high cost. Moreover, ametal shield has a problem of easy oxidation. A metal shield avoids thedisturbance by means of reflecting electromagnetic waves, however, asfor some other application fields such as national defense,electromagnetic waves should be shielded by means of absorbing them. Onthe other hand, the method of infilling conductive materials in plasticcasing has problems such as bad efficiency of shielding and difficultiesin recycling plastic casings. To summarize, a material with lowpollution, high conductivity, microwave absorption, and capable ofcoated on a large area could solve the problems mentioned above.

Electromagnetic shielding effect is related to the absorbing andreflecting ability of a material. A metal shield has high density offree charge on its surface, so when electromagnetic waves incident thesurface of a metal, most of the electro-magnetic waves will bereflected. Therefore, a metal shield avoids the disturbance by means ofreflecting electromagnetic waves.

When electromagnetic waves incident a conductive high polymer, theconductive high polymer generates an induced current corresponding tothe electromagnetic waves and transforms the electric energy to heat bymeans of the flowage of the induced current to deplete the energy of theelectromagnetic waves. Thereby, a conductive high polymer could avoidthe disturbance by means of absorbing electromagnetic waves. Among allkinds of conductive high polymers, the polyaniline, which is a materialwith high potential, has advantages of high conductivity, cheap rawmaterials, high stability, and easy fabrication.

Otherwise, the carbon nanotube has fine physical, mechanical, chemical,and electric characteristics as well as high stability, so it is widelyapplied to various fields. Moreover, a composite is composed of two ormore materials with different material characteristics by means ofphysical or chemical combination, so the composite not only has betterproperty than any one of the composition but also keeps every singlematerial's origin characteristic. Practically, nanocomposite has becomean important issue for researchers from all over the world because ofits enormous potential. A composite including carbon nanotubes thereinsucceeds to the characteristic of the carbon nanotube, and it issupposed to have high value.

However, the carbon nanotubes tend to entwine each other owing to theirown van der waals force. And also because the chemical stability, thereis no functional groups on the surface of the carbon nanotube, so thatthey are difficultly dissolved or dispersed in organic solvent or water.The above-mentioned characteristics of carbon nanotubes are problemswaiting to be improved.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention is to provide a methodfor fabricating a polyaniline/c-MWNT nanocomposite which the carboxyliccarbon nanotubes disperse in the polyaniline to form thepolyaniline/c-MWNT nano-composite that could be used for electromagneticshielding or anti-static shielding to solve the problems mentionedabove.

According to an embodiment of the invention, the method for fabricatinga polyaniline/c-MWNT nanocomposite comprises the following steps:firstly, carboxylating at least one carbon nanotube to form at least onecarboxylic carbon nanotube; then mixing the at least one carboxyliccarbon nanotube with a solvent to form a first carbon nanotube solution;subsequently, mixing at least one aniline monomer with the first carbonnanotube solution to form a second carbon nanotube solution; next,mixing an ammonium persulfate solution with the second carbon nanotubesolution to form a third carbon nanotube solution; after that,air-extracting and filtering the third carbon nanotube solution toobtain the polyaniline/c-MWNT nanocomposite; finally, cleaning andbaking the polyaniline/c-MWNT nanocomposite.

In the embodiment, the carbon nanolubes could be mixed with a sulfuricacid/nitric acid solution and ultrasonic vibrated to obtain thecarboxylic carbon nanotubes. There are functional groups on the surfacesof the carboxylic carbon nanotubes and the functional groups increasethe solvability of the carboxylic carbon nanotubes in an organic solventor water. The at least one aniline monomer is mixed with the carboxyliccarbon nanotubes in the solvent and processed with appropriate treatment(e.g. ice bathed or agitated) to form the second carbon nanotubesolution. The second carbon nanotube solution is then reacted with theammonium persulfate solution (initiator) to form the polyaniline.Meanwhile, the carboxylic carbon nanotubes are dispersed in thepolyaniline to produce the polyaniline/c-MWNT nanocomposite. The thirdcarbon nanotube solution after reacted with the ammonium persulfatesolution (initiator) is filtered, and the filtered products are cleanedand baked to obtain the polyaniline/c-MWNT nanocomposite.

Another aspect of the present invention is to provide a polymercomposite which could be used for electromagnetic shielding oranti-static shielding.

In an embodiment, the polymer composite of the invention comprises apolyaniline and carboxylic carbon nanotubes dispersing in thepolyaniline. The carboxylic carbon nanotubes are obtained by means ofcarboxylating carbon nanotubes, wherein the steps of carboxylatinginclude the following steps: mixing the carbon nanotubes with a sulfuricacid/nitric acid solution and ultrasonic vibrating the mixed solution ofthe carbon nanotubes and the sulfuric acid/nitric acid solution toobtain the carboxylic carbon nanotubes. There are functional groups onthe surfaces of the carboxylic carbon nanotubes and the functionalgroups increase the solvability of the carboxylic carbon nanotubes in anorganic solvent or water.

In the embodiment, an aniline monomer could be mixed with carboxyliccarbon nanotubes in a solvent and processed with appropriate treatment(e.g. ice bathed or agitated) to form a solution of carboxylic carbonnanotubes with the aniline monomer. An ammonium persulfate solution(initiator) is mixed with the solution mentioned above to make theaniline monomer to form the polyaniline. Simultaneously, the carboxyliccarbon nanotubes are dispersed in the polyaniline. Subsequently, themixed solution is filtered and then the polyaniline/c-MWNT nanocompositewith carboxylic carbon nanotubes dispersing in the polyaniline isobtained. The polyaniline/c-MWNT nanocomposite is the polymer compositeof the invention.

The objective of the present invention will no doubt become obvious tothose of ordinary skill in the art after reading the following detaileddescription of the preferred embodiment, which is illustrated in thevarious figures and drawings.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 is a flow chart illustrating a method for fabricating apolyaniline/c-MWNT nano-composite according to an embodiment of theinvention.

FIG. 2 is a flow chart illustrating the process of carboxylating thecarbon nanotubes in FIG. 1.

FIG. 3 illustrates the structure of part surface of a carboxylic carbonnanotube according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Please refer to FIG. 1. FIG. 1 is a flow chart illustrating a method forfabricating a polyaniline/c-MWNT nano-composite according to anembodiment of the invention. The polyaniline/c-MWNT nanocompositefabricated by means of the method of the embodiment could be coated onshielding casings of electronic devices as a material forelectromagnetic shielding or anti-static shielding.

As illustrated in FIG. 1, the fabricating method of the embodimentincludes the following steps. In step S10, carbon nanotubes arecarboxylated to form carboxylic carbon nanotubes. In step S12, thecarboxylic carbon nanotubes are mixed with a solvent to form a firstcarbon nanotube solution. In step S14, aniline monomers are mixed withthe first carbon nanotube solution to form a second carbon nanotubesolution. In step S16, an ammonium persulfate solution is mixed with thesecond carbon nanotube solution to form a third carbon nanotubesolution. Finally, in step S18, the third carbon nanotube solution isair-extracted and filtered to obtain the polyaniline/c-MWNTnanocomposite, and the polyaniline/c-MWNT nanocomposite is cleaned andbaked.

Practically, all of the solutions formed in the steps mentioned abovecould be processed a treatment, depending on the requirement, to helpthe aniline monomers and the carboxylic carbon nanotubes dissolvedtherein. For example, the first carbon nanotube solution could beagitated for a night to make the carboxylic carbon nanotubes dissolvedtherein. Moreover, the second carbon nanotube solution could be icebathed and agitated for 0.5 hour to make the aniline monomers dissolvedtherein. Furthermore, the third carbon nanotube solution could be icebathed and agitated for 3 hours to make the ammonium persulfate solutioncompletely mixed with the second carbon nanotube solution mentionedabove.

In the embodiment, because there is no interaction force existingbetween the carbon nanotubes and the polymer composite, and also thereis no functional group on the surface of the carbon nanotube, the carbonnanotube is difficultly dispersed in the polyaniline and combined withthe polyaniline. In the step S10, after carboxylating the carbonnanotubes, the carboxylic carbon nanotubes possesses higher solvabilitybecause of the —COOH functional groups on the surface thereof whichhelps the carboxylic carbon nanotube dispersed in the polyaniline andcombined with the polyaniline.

Please refer to FIG. 2. FIG. 2 is a flow chart illustrating the processof carboxylating the carbon nanotubes in FIG. 1. As illustrated in FIG.2, the process includes the following steps. In step S100, the carbonnanotubes are mixed with a sulfuric acid/nitric acid solution to form amixed solution. In step S102, the mixed solution is ultrasonic vibrated.In step S104, the mixed solution is filtered to obtain the carboxyliccarbon nanotubes, and the carboxylic carbon nanotubes obtained iscleaned and baked.

Practically, the carbon nanotubes mentioned above could be, but notlimited to, multi-wall carbon nanotubes. The ratio of the sulfuric acidto the nitric acid of the sulfuric acid/nitric acid solution in the stepS100 could be 3:1 in practical applications, wherein the concentrationof the sulfuric acid therein could be 90% wt and that of the nitric acidtherein could be 70% wt. The process of ultrasonic vibrating the mixedsolution in the step S102 could be under the temperature range of 20±5°C. in the embodiment, however, the range of the temperature could dependon the requirement of users, but not limited to the embodiment of theinvention. Moreover, the ultrasonic vibrating time could depend onusers' requirement as well, but not limited to a specific period oftime. For example, the mixed solution could be ultrasonic vibrated underthe temperature range of 20÷5° C. for 4, 8, 12, or 24 hours. Pleasenotice that the ultrasonic vibrating is for assisting the carbonnanotube in forming —COOH functional groups on the surface of the carbonnanotubes to increase solvability of the carbon nanotubes in thesolvent. Thus, the longer the ultrasonic vibrating time is, the easierit is for the carboxylic carbon nanotube to be dissolved in the solvent.However, forming —COOH functional groups on the surface of the carbonnanotubes means that the sp2 bonding thereon would be damaged, thus thelonger the ultrasonic vibrating time is, the lower the conductivity ofthe carboxylic carbon nanotubes is.

Please refer to FIG. 3. FIG. 3 illustrates the structure of part surfaceof a carboxylic carbon nanotube 2 according to an embodiment of theinvention. As illustrated in FIG. 3, the surface of the carboxyliccarbon nanotube 2 is constructed by hexagonal structure 20. Thedifference between the carboxylic carbon nanotube 2 and the commoncarbon nanotube is that some of the sp2 bonding of the hexagonalstructure 20 is damaged and connected with —COOH functional group 22.Practically, the longer the ultrasonic vibrating time is, the larger thenumber of the —COOH functional group 22 is.

The filtered carboxylic carbon nanotubes in the step S106 in theembodiment could be cleaned by deionized water and methanol repeatedlyfor several times and then baked in an oven under 60° C. for 24 hours toget rid of extra water of the carboxylic carbon nanotubes. Similarly,the cleaning fluid, the temperature of the oven and the baking timecould be adjusted according to the requirement of users, but not limitedto the embodiment of the invention.

Please refer to FIG. 1 again. The composition of the solvent mixed withthe carboxylic carbon nanotubes in the step S12 in FIG. 1 could behydrogen chloride. Subsequently, in the step S14 the aniline monomersare mixed with the first carbon nanotube solution in the step S12 toform a second carbon nanotube solution. In the step S16 the ammoniumpersulfate solution is mixed with the second carbon nanotube solution toform a third carbon nanotube solution. In the step S18 thepolyaniline/c-MWNT nanocomposite is filtered and obtained from the thirdcarbon nanotube solution and then cleaned and baked.

In the embodiment, the polyaniline formed from the aniline monomers bymeans of the steps mentioned above is an emeraldine base form ofpolyaniline. A common emeraldine base form of polyaniline has conjugateddouble bonds. However, such form of polyaniline lacks of free chargeresulting in bad conductivity, so the polyaniline needs providing withfree charge on the conjugated double bonds by means of doping to improveits conductivity. In the embodiment, the first carbon nanotube solutionwhich is mixed with the aniline monomers includes hydrogen chloride(namely, polyaniline dopant). The polyaniline doped with low pH valueprotic acid has much higher conductivity and is suitable forelectromagnetic shielding or anti-static shielding. Similarly, the dopedprotic acid, as a dopant which increases the conductivity of thepolyaniline, could be other inorganic acids such as phosphoric acid inpractical applications.

On the other hand, the ammonium persulfate in the step S16 of theembodiment is used as an initiator to assist the aniline monomers withpolymerization to form the polyaniline. In the embodiment, the ammoniumpersulfate solution is a mixture of ammonium persulfate and hydrochloricacid.

According to another embodiment, the polymer composite of the inventioncould include a polyaniline/c-MWNT nanocomposite, wherein thepolyaniline/c-MWNT nanocomposite further includes a polyaniline andcarboxylic carbon nanotubes dispersing in the polyaniline, which couldbe formed by means of the fabricating method disclosed above, so thedetails of the fabricating method are not described again here.

In the embodiment, there are functional groups on the surfaces of thecarboxylic carbon nanotubes so that the carboxylic carbon nanotubescould disperse in the polyaniline during the process of fabricating thepolymer composite, unlike uncarboxylic carbon nanotubes untwine eachother which are difficultly dispersed. Moreover, during the process offabricating the polyaniline of the polyaniline/c-MWNT nanocomposite, aninorganic acid, such as hydrogen chloride or phosphoric acid, is dopedto provide the polyaniline with free charge on the conjugated doublebonds thereof to improve the conductivity of the polyaniline.

Because a polymer composite will have the characters of the originalmaterials, the polyaniline/c-MWNT nanocomposite of the embodiment willhave good conductivity as the doped polyaniline and the carbon nanotube.The polyaniline/c-MWNT nanocomposite could be coated on casings ofelectronic devices for electromagnetic shielding or anti-staticshielding to protect electronic devices against the disturbance ofelectromagnetic waves or static electricity. Otherwise, thepolyaniline/c-MWNT nanocomposite keeps the physical characteristics andchemical characteristics of the polyaniline and the carbon nanotubethose make the polyaniline/c-MWNT nanocomposite could be applied totheir original application domains respectively.

Compared to the prior art, the polymer composite and the fabricatingmethod for making the same of the invention could provide functionalgroups on the surfaces of the carboxylic carbon nanotubes that help thecarboxylic carbon nanotubes with dispersing in the polyaniline to formthe polyaniline/c-MWNT nanocomposite. The polyaniline is doped with lowpH value protic acid while fabricating that makes it has much higherconductivity. Moreover, the carbon nanotube itself has good conductivityas well. All that makes the polyaniline/c-MWNT nanocomposite suitable asa conductive coating material to protect electronic devices against thedisturbance of electromagnetic wave or static electricity, so as toaffectively extend the lifetime of electronic devices.

Although the present invention has been illustrated and described withreference to the preferred embodiment thereof, it should be understoodthat it is in no way limited to the details of such embodiment but iscapable of numerous modifications within the scope of the appendedclaims.

1. A method for fabricating a polyaniline/c-MWNT nanocomposite,comprising the following steps: carboxylating at least one carbonnanotube to form at least one carboxylic carbon nanotube; mixing the atleast one carboxylic carbon nanotube with a solvent to form a firstcarbon nanotube solution; mixing at least one aniline monomer with thefirst carbon nanotube solution to form a second carbon nanotubesolution; mixing an ammonium persulfate solution with the second carbonnanotube solution to form a third carbon nanotube solution;air-extracting and filtering the third carbon nanotube solution toobtain the polyaniline/c-MWNT nanocomposite; and cleaning and baking thepolyaniline/c-MWNT nanocomposite.
 2. The method of claim 1, wherein thecarboxylic carbon nanotubes of the polyaniline/c-MWNT nanocompositedisperse in the polyaniline.
 3. The method of claim 1, furthercomprising the following steps: mixing at least one carbon nanotube witha sulfuric acid/nitric acid solution to form a mixed solution;ultrasonic vibrating the mixed solution; air-extracting and filteringthe mixed solution to obtain at lease one carboxylic carbon nanotube;and cleaning and baking the carboxylic carbon nanotubes.
 4. The methodof claim 3, wherein the ratio of the sulfuric acid to the nitric acid ofthe sulfuric acid/nitric acid solution is 3:1.
 5. The method of claim 3,wherein the mixed solution is ultrasonic vibrated under the temperaturerange of 20±5° C.
 6. The method of claim 1, wherein the composition ofthe solvent is hydrochloric acid, namely, hydrogen chloride.
 7. Themethod of claim 1, wherein the ammonium persulfate solution is a mixtureof ammonium persulfate and a first solvent.
 8. The method of claim 7,wherein the composition of the first solvent is substantially the sameas that of the solvent.
 9. The method of claim 1, wherein thepolyaniline/c-MWNT nanocomposite comprises an emeraldine base form ofpolyaniline.
 10. A polymer composite, comprising: a polyaniline; and atleast one carboxylic carbon nanotube dispersing in the polyaniline; 11.The polymer composite of claim 10, wherein the fabrication of thecarboxylic carbon nanotubes is mixing at least one carbon nanotubes witha sulfuric acid/nitric acid solution to form a mixed solution,ultrasonic vibrating the mixed solution, and filtering the mixedsolution to obtain the at lease one carboxylic carbon nanotube.
 12. Thepolymer composite of claim 11, wherein the ratio of the sulfuric acid tothe nitric acid of the sulfuric acid/nitric acid solution is 3:1. 13.The polymer composite of claim 11, wherein the mixed solution isultrasonic vibrated under the temperature range of 20±5° C.
 14. Thepolymer composite of claim 10, wherein the carboxylic carbon nanotubesare dispersed in the polyaniline by means of the following steps; mixingthe at least one carboxylic carbon nanotube with a solvent to form afirst carbon nanotube solution; mixing at least one aniline monomer withthe first carbon nanotube solution to form a second carbon nanotubesolution; mixing an ammonium persulfate solution with the second carbonnanotube solution to form a third carbon nanotube solution; andair-extracting and filtering the third carbon nanotube solution toobtain the polymer composite thereof the at least one carboxylic carbonnanotube disperse in the polyaniline.
 15. The polymer composite of claim14, wherein the composition of the solvent is hydrochloric acid, namely,hydrogen chloride.
 16. The polymer composite of claim 14, wherein theammonium persulfate solution is a mixture of ammonium persulfate and afirst solvent.
 17. The polymer composite of claim 16, wherein thecomposition of the first solvent is substantially the same as that ofthe solvent.
 18. The polymer composite of claim 10, wherein thepolyaniline is an emeraldine base form of polyaniline.